1. Field of the Invention
The present invention relates to an electrical machining medium to be interposed between an electrode and a workpiece in electrical discharge machining. In another aspect, the present invention relates to an electrical discharge machining method employing such a processing medium.
2. Description of the Prior Art
Electrical discharge machining is a production technique which comprises causing a spark discharge to take place intermittently in an insulating medium between a tool electrode and a conductive workpiece to thereby carve, drill or cut the workpiece. Because this technique is not dependent on the hardness of the workpiece and is capable of providing a machining accuracy close to mirror finish with a surface roughness of .+-.0.2 .mu.m or less, it is widely used today in metal working.
Heretofore, a mineral oil (kerosene) has been mainly used as said insulating medium. However, as this mineral oil is inflammable, there is the risk of fire hazards in no-man continuous operations. Therefore, the use of pure water has been attempted recently. However, although water offers the advantage of high machining speed, it is disadvantageous in that it causes a premature electrode consumption. Recently, therefore, the addition of various auxiliary agents to water has been contemplated. For example, there has been proposed the addition of glycols such as ethylene glycol, propylene glycol, polyethylene glycol, polyalkylene glycol ether, etc., derivatives thereof, non-ionic materials such as higher alcohols, acrylamide, polyacrylamide, guar gum, etc., anionic substances such as polyacrylic acid, polymethacrylic acid, sodium alginate, etc., or cationic substances such as chitosan [See, for example, Japanese Patent Publication No. 59-4253.]
However, even with such contrivances, the electrode consumption rate can be reduced only by 3 percent at best [See FIG. 2 of the above publication]. However, in order to assure a sufficient machining accuracy in carving or drilling, it is an absolute requirement that the electrode consumption rate is less than 1 percent at most. Therefore, all of the conventional aqueous media are unsatisfactory for practical purposes.